During my last holiday to the East Coast of Malaysia, I had some wonderful Malaysian food at Pasar Payang, Kuala Terengganu. One of the yummy Malaysian delicacies I had was 'tapai pulut' or fermented glutinous rice. It is very popular among Malaysians and normally eaten as dessert. Tapai pulut is an everyday dessert served at functions such as festivals and weddings usually by the Malay community in Malaysia. The taste is sweet with a pleasant aroma and it is wrapped in rubber tree leaves. Sometimes, it is also wrapped in banana leaves.
|Tapai Pulut in banana leaves|
Tapai Pulut is made by fermenting glutinous rice (Oryza sativa glutinosa). What exactly is fermentation though? Fermentation is an anaerobic process in which energy can be released from glucose even though oxygen is not available.
My curiosity encouraged me to do further research on how Tapai Pulut is made. After reading a few articles and asking my mother, here are the steps:-
1. First, wash the glutinous rice and soak it overnight
2. Next, cook the glutinous rice
3. When the rice is cooked, cool it
4. Pound the yeast. Sprinkle it on top of the cooked rice
5. Turn the rice over and sprinkle yeast on it
6. Put the rice in an air tight container and let it ferment for 2 days
7. After 2 days, the rice is ready to be wrapped in rubber tree leaves
8. Keep it in the refrigerator until cool.
9. It’s now ready to be eaten and enjoyed!
Why do you think yeast is necessary? Yeast carries out both aerobic respiration and anaerobic respiration. Aerobic respiration takes place in the presence of oxygen while anaerobic respiration refers to the type of respiration that takes place in the absence of oxygen. Anaerobic respiration in yeast cells is called fermentation. During fermentation, yeast secretes the enzyme zymase which hydrolyses glucose in the absence of oxygen to form ethanol, carbon dioxide and energy.
Glucose → ethanol + carbon dioxide + energy
C6H12O6 → 2C2H5OH + 2CO2 + energy
The enzyme zymase by the yeast speeds up the fermentation process. In the fermentation process, only a small amount of energy is released. A large amount of energy is still stored in ethanol as chemical energy. This is because glucose is not completely broken down in anaerobic respiration. The products of fermentation such as carbon dioxide, is used as a raising agent in baking bread while ethanol is used to produce alcoholic drinks such as wine.